1. Field of the Invention
The present invention relates to a signal processing device which performs noise canceling by subjecting sound-collected sound signals from a sound-collecting unit to filtering processing so as to provide signal properties for noise reduction, thereby performing noise canceling operations.
2. Description of the Related Art
There is in practical use a so-called noise canceling system for headphone devices, arranged to actively cancel external noise which can be heard when playing audio contents such as tunes and the like with the headphone devices. Such noise canceling systems can be generally classified into the two methods of the feedback method and the feed-forward method.
For example, Japanese Unexamined Patent Application Publication No. 3-214892 describes the configuration of a noise canceling system having a configuration wherein external noise can be reduced by generating audio signals with inverted phase of noise within a tube mounted to the ears of the user that is sound-collected by a microphone unit provided nearby the earphone (headphone) unit, and outputting this as sound from the earphone unit, i.e., a noise canceling system configuration corresponding to the feedback method.
Also, Japanese Unexamined Patent Application Publication No. 3-96199 describes a basic configuration wherein audio signals obtained by sound-collecting with a microphone attached to an outer housing of a headphone device are provided with a predetermined transfer function and output from the headphone device, i.e., a noise canceling system configuration corresponding to the feed-forward method.
In employing either of the feed-forward method or feedback method, filter properties set for noise canceling are set such that noise is canceled (reduced) at the ear position of the user, based on spatial transfer functions regarding audio from an external noise source arriving at the ear position of the user (noise cancellation point), properties of electrical parts such as microphone amp, headphone amp, and so forth and further, various types of transfer functions such as properties of acoustic parts such as microphone, driver unit (speaker), and so forth for example.